Abnormalities of the optic disc

Effect of changes in optic nerve elasticity on central retinal artery blood flow in patients with idiopathic intracranial hypertension

PURPOSE

To assess changes in central retinal artery (CRA) blood flow by orbital color-coded Doppler ultrasonography in patients with idiopathic intracranial hypertension (IIH) and their relation with optic nerve (ON) elasticity assessed by shear wave elastography (SWE).

METHODS

This study was carried out on 68 eyes of patients diagnosed with IIH and 32 eyes of healthy controls. The severity of papilledema in IIH patients was sub-classified into mild and moderate/severe groups. Color-coded Doppler was used to measure peak systolic velocity (PSV), end diastolic velocity (EDV), mean velocity (V_mean) and pulsatility index (PI) of the CRA.

RESULTS

PSV, V_mean, and SWE were significantly higher in patients with IIH than in controls (p = 0.001). The optimal cut-off values of PSV and V_mean for differentiating IIH patients from controls were 11.25 and 6.75 cm/s with AUC 0.81 and 0.785 respectively. AUC was 0.92 and accuracy 91% for combined PSV, V_mean and SWE differentiation between IIH patients and controls. PSV, V_mean and SWE were significantly different between mild versus moderate/severe papilledema (p = 0.001). PSV and V_mean were correlated with papilledema (r = 0.790 and 0.722 respectively) and SWE (r = 0.818 and 0.761 respectively).

CONCLUSION

IIH is associated with decreased ON elasticity and reduced CRA blood flow. Individual and combined color-coded Doppler of the CRA and SWE help in diagnosis of IIH. CRA hemodynamic changes are correlated with papilledema severity and with the extent of biomechanical changes in the ON represented by SWE.

A Deep-Learning Approach for Automated OCT En-Face Retinal Vessel Segmentation in Cases of Optic Disc Swelling Using Multiple En-Face Images as Input

Purpose

In cases of optic disc swelling, segmentation of projected retinal blood vessels from optical coherence tomography (OCT) volumes is challenging due to swelling-based shadowing artifacts. Based on our hypothesis that simultaneously considering vessel information from multiple projected retinal layers can substantially increase vessel visibility, in this work, we propose a deep-learning-based approach to segment vessels involving the simultaneous use of three OCT en-face images as input.

Methods

A human expert vessel tracing combining information from OCT en-face images of the retinal pigment epithelium (RPE), inner retina, and total retina as well as a registered fundus image served as the reference standard. The deep neural network was trained from the imaging data from 18 patients with optic disc swelling to output a vessel probability map from three OCT en-face input images. The vessels from the OCT en-face images were also manually traced in three separate stages to compare with the performance of the proposed approach.

Results

On an independent volume-matched test set of 18 patients, the proposed deep-learning-based approach outperformed the three OCT-based manual tracing stages. The manual tracing based on three OCT en-face images also outperformed the manual tracing using only the traditional RPE en-face image.

Conclusions

In cases of optic disc swelling, use of multiple en-face images enables better vessel segmentation when compared with the traditional use of a single en-face image.

Translational Relevance

Improved vessel segmentation approaches in cases of optic disc swelling can be used as features for an improved assessment of the severity and cause of the swelling.

Optical coherence tomography and neurodegeneration: are eyes the windows to the brain?

INTRODUCTION

Central nervous system (CNS) pathologies have ocular manifestations due to direct and/or retrograde degeneration of the visual pathways, most often related to a direct injury to the optic nerve, retinal ganglion cells and/or its surrounding cells. These ocular manifestations can be recognized and monitored by a non-invasive technique called Optical Coherence Tomography (OCT).

AREAS COVERED

This review article describes the OCT technique and its application in various neurological pathologies. OCT helps in the measurement of retinal nerve fiber layer thickness (RNFLT) and macular thickness which consists of retinal ganglion cells. OCT provides a near-histological level of image resolution up to 5µm by using principles of interferometry that can detect CNS inflammatory, as well as degenerative, pathologies (i.e Multiple Sclerosis, Parkinson's disease and Alzheimer's Disease etc.) at initial clinical and possibly subclinical stages. Expert Commentary: RNFLT and macular volumes measured by OCT can serve as biomarkers for early recognition and progression of a variety of neurological disease, although the specificity of these findings in clinical diagnosis requires further refinement. An early biomarker can help in an earlier therapeutic intervention and thus preventing further progression and provide the opportunity for possible regenerative interventions of the underlying disease process. With the advent of "next-generation" OCT technology an increase in use is foreseen in research as well as in clinical practice.

The usefulness of multimodal imaging for differentiating pseudopapilloedema and true swelling of the optic nerve head: a review and case series

Ophthalmic practitioners have to make a critical differential diagnosis in cases of an elevated optic nerve head. They have to discriminate between pseudopapilloedema (benign elevation of the optic nerve head) and true swelling of the optic nerve head. This decision has significant implications for appropriate patient management. Assessment of the optic disc prior to the advanced imaging techniques that are available today (particularly spectral domain optical coherence tomography and fundus autofluorescence), has mainly used diagnostic tools, such as funduscopy and retinal photography. As these traditional methods rely on the subjective assessment by the clinician, evaluation of the elevated optic nerve head to differentiate pseudopapilloedema from true swelling of the optic nerve head can be a challenge in clinical practice with patients typically referred for further neuroimaging investigation when the diagnosis is uncertain. The use of multimodal ocular imaging tools such as spectral domain optical coherence tomography, short wavelength fundus autofluorescence and ultrasonography, can potentially aid in the differentiation of pseudopapilloedema from true swelling of the optic nerve head, in conjunction with other clinical findings. By doing so, unnecessary patient costs and anxiety in the case of pseudopapilloedema can be reduced, and appropriate urgent referral and management in the case of true swelling of the optic nerve head can be initiated.

Anatomical and functional impairment of the nerve fiber layer in patients with optic nerve head drusen

OBJECTIVE

To evaluate anatomical and functional impairment of the retinal nerve fiber layer (RNFL) using optical coherence tomography (OCT) and automated perimetry in patients with optic nerve head drusen (ONHD).

MATERIALS AND METHODS

Sixty-six eyes (66 patients) were studied with ONHD - confirmed by ultrasound B scan - and 70 eyes (70 subjects) of healthy control subjects. ONHD cases were categorised as visible or hidden. Average RNFL thickness and measurements in terms of the quadrants were analysed using both time-domain optical coherence tomography (TD-OCT) and spectral-domain optical coherence tomography (SD-OCT). Anatomical and visual field alteration of RNFL between visible and hidden ONHD and control groups were compared.

RESULTS

Average RNFL thickness in ONHD patients was 94 μm (TD-OCT) and 88 μm (SD-OCT), and in controls 107 μm (TD-OCT) and 96 μm (SD-OCT), with statistically significant differences between both OCTs. All quadrants analysed showed significant differences except the temporal quadrant. The differences were not significant between hidden drusen and controls.Visual field examination in ONHD showed alterations in 56 %. Alterations were greater in visible drusen in relation to non-visible drusen, but there were no significant differences.The association between RNFL defects in superior, inferior and temporal quadrants and visual field defects showed a statistical relation with visible ONHD, but not in hidden ONHD.

CONCLUSIONS

ONHD caused anatomical and functional damage of the RNFL, with a clear association between the alteration in ONHD and visual field defects in visible drusen cases.

The role of the physical examination in the evaluation of headache

The population of patients suffering with headaches is vast and underserved. The most critical element in headache evaluation is the history. The targeted history not only differentiates primary from secondary headaches but also provides a realistic list of conditions associated with secondary headache. Several of these conditions do present with specific physical findings, such as papilledema, Horner's syndrome, or CN palsy. The targeted physical examination of the patient with headache takes less than 3 minutes. The ability simply to recognize but a few straightforward clinical findings directs the evaluation in the proper direction. If you enjoy seeing patients, feel competent identifying but a few physical findings, and understand the basics of primary and secondary headaches and facial pain, there is urgent need of your services.

Patterns of ganglion cell complex and nerve fiber layer loss in nonarteritic ischemic optic neuropathy by Fourier-domain optical coherence tomography

PURPOSE

To characterize by Fourier-domain optical coherence tomography (FD-OCT) the loss of nerve fiber layer (NFL) and ganglion cell complex (GCC) in nonarteritic ischemic optic neuropathy (NAION).

METHODS

Patients diagnosed with NAION were enrolled and categorized into "superior field loss (SFL)," "inferior field loss (IFL)," and "bihemispheric field loss (BFL)" groups based on the Swedish interactive threshold algorithm 30-2 achromatic visual field (VF) tests. Six months after presentation, they were scanned by FD-OCT to map peripapillary NFL and macular GCC thicknesses. Age-matched normals were selected from participants in the Advanced Imaging for Glaucoma Study (www.AIGStudy.net). Deviation maps were defined as the difference between the thickness maps and the average normal maps. Pearson's correlation coefficient was used to assess the correlation between VF and OCT measurements.

RESULTS

Twenty-five NAION eyes in 20 subjects were analyzed. Most (2/3) SFL cases showed inferior NFL loss with variable sparing of inferonasal losses. All (4/4) IFL cases showed superior NFL loss with variable inferonasal extension. The GCC maps demonstrated clear hemispheric loss pattern in agreement with VFs. NFL and GCC losses could be detected even in the less affected hemispheres (P < 0.001). NFL and GCC were highly correlated (P < 0.001) with VF in terms of both overall averages and superior-inferior hemispheric differences.

CONCLUSIONS

NFL and GCC losses correlated well with VF losses in both magnitude and location. Hemispheric GCC loss correlated with altitudinal VF loss and this pattern may be of diagnostic value. FD-OCT is useful in the evaluation of NAION.

Traumatology of the optic nerve and contribution of crystallins to axonal regeneration

Within a few decades, the repair of long neuronal pathways such as spinal cord tracts, the optic nerve or intracerebral tracts has gone from being strongly contested to being recognized as a potential clinical challenge. Cut axonal stumps within the optic nerve were originally thought to retract and become irreversibly necrotic within the injury zone. Optic nerve astrocytes were assumed to form a gliotic scar and remodelling of the extracellular matrix to result in a forbidden environment for re-growth of axons. Retrograde signals to the ganglion cell bodies were considered to prevent anabolism, thus also initiating apoptotic death and gliotic repair within the retina. However, increasing evidence suggests the reversibility of these regressive processes, as shown by the analysis of molecular events at the site of injury and within ganglion cells. We review optic nerve repair from the perspective of the proximal axon stump being a major player in determining the successful formation of a growth cone. The axonal stump and consequently the prospective growth cone, communicates with astrocytes, microglial cells and the extracellular matrix via a panoply of molecular tools. We initially highlight these aspects on the basis of recent data from numerous laboratories. Then, we examine the mechanisms by which an injury-induced growth cone can sense its surroundings within the area distal to the injury. Based on requirements for successful axonal elongation within the optic nerve, we explore the models employed to instigate successful growth cone formation by ganglion cell stimulation and optic nerve remodelling, which in turn accelerate growth. Ultimately, with regard to the proteomics of regenerating retinal tissue, we discuss the discovery of isoforms of crystallins, with crystallin beta-b2 (crybb2) being clearly upregulated in the regenerating retina. Crystallins are produced and used to promote the elongation of growth cones. In vivo and in vitro, crystallins beta and gamma additionally promote the growth of axons by enhancing the production of ciliary neurotrophic factor (CNTF), indicating that they also act on astrocytes to promote axonal regrowth synergistically. These are the first data showing that axonal regeneration is related to crybb2 movement within neurons and to additional stimulation of CNTF. We demonstrate that neuronal crystallins constitute a novel class of neurite-promoting factors that probably operate through an autocrine and paracrine mechanism and that they can be used in neurodegenerative diseases. Thus, the post-injury fate of neurons cannot be seen merely as inevitable but, instead, must be regarded as a challenge to shape conditions for initiating growth cone formation to repair the damaged optic nerve.